We originally created Simplenote both as a learning exercise and to address what we thought were shortcomings in the original Notes app for the iPhone (Marker Felt font, no ability to search, etc.) The very first version of Simplenote didn't even have syncing!

We've certainly come a long way since then. The Simplenote backend now synchronizes data across devices, the web, and third-party apps while also handling in-app purchases, sharing, and basic metrics. About a year ago, we were accepted to the Y Combinator startup accelerator with something like 20,000 users. Today, with hundreds of thousands of users, we're currently serving 15 million requests daily and providing access to over 500 gigabytes (!) worth of text notes.

Google App Engine is at the heart of it. We made a decision early on to use App Engine so we wouldn't have to worry about scaling, or deploying more servers, or systems administration of any kind. Being able to instantly deploy new versions of code has allowed us to iterate quickly based on feedback we get from our users, and easily test new features in our web app, like the newly added Markdown support.

We consider our syncing capabilities to be core features of Simplenote. They are, in and of themselves, largely responsible for attracting and retaining many of our users. Our goal is to give other developers access to great syncing, too. The next version of our backend is named after our company, Simperium. As a general-purpose, realtime syncing platform intended for third-party use, Simperium's architecture is much more expansive than the Simplenote backend. Yet App Engine still plays a key role. It powers the Simplenote API that is used by dozens of great third-party apps like Notational Velocity. And it continues to power auxiliary systems, like processing payments with Stripe, while bridging effectively with externally hosted systems, like our solution for storing notes as files in the wonderful Dropbox.

We suspected we might outgrow App Engine, but we haven't. Instead, our use of it has evolved along with our needs. Code we wrote for App Engine a year ago continues to hum along today, providing important functionality even as new systems spring up around it.

In fact, we still come up with entirely new ways to use App Engine as well. Just last week we launched an internal system that uses APIs from Twitter, Amazon Web Services, Assistly, and HipChat to pump important business data into our private chat rooms. This was a breeze to write and deploy using App Engine. Such is the mark of a versatile and trustworthy tool: it's the first thing you reach for in your tool belt.